Antenna computing means



Dec. 30, 1958 J. P. SHANKLIN 2,866,968

ANTENNA COMPUTING MEANS Filed Nov. 13, 1956 2 Sheets-Sheet l Del-Ecr01? 0544 y LINE By M/myft Saran/n1; ExEcurR/x BY w w 4 Dec. 30, 1958 J. P. SHANKLIN 2,866,968

ANTENNA COMPUTING MEANS Filed Nov. 13, 1956 2 Sheets-Sheet? FIEK F Rsc NVENTOR. JOHN P SHOW/fl. 11v, Dacznsso,

By MnRY H SHnN/n. IN, ExcurR1x,

BY 2% Q 9 g Z ANTENNA COMPUTING MEANS John P. Shanklin, deceased, late of Cedar Rapids, Iowa, by

Mary H. Shanklin, executrix, Cedar Rapids, Iowa, assignor to Collins Radio Company, Cedar Rapids, Iowa, a corporation of Iowa Application November 13, 1956, Serial No. 621,739

12 Claims. (Cl. 343100) This invention relates to means for computing and con- 15 trolling a radiation pattern provided by an array of antennas.

Often, it is necessary to provide an antenna array to obtain a required radiation pattern. Three important variables involved are: the positions of the antennas in 20 the array with respect to each other in wavelengths, the respective phase shifts caused by transmission lines connected to the antennas, and the respective energy intensities at the antennas.

Large antennas involve considerable expense, an economy dictates that they be positioned properly in an array when it is initially constructed. For example, it may be required to obtain an antenna array having a particular pattern, wherein each antenna in the array is a low-frequency omnidirectional antenna that must be positioned on an immovable tower.

This invention teaches how a device of relatively simple construction can be made that enables a convenient and relatively inexpensive determination of the energy intensities, transmission-line phasing, and positions of the respective antennas in an array with very little error.

Furthermore, this invention teaches how the same type of device can also be used as a means for rotating the radiation pattern of an array to any azimuth angle.

It is, accordingly, an object of this invention to provide a computer for determining the radiation pattern of an array of antennas, wherein the array may have any number of component antennas which may have any position with respect to each other within the array.

It is another object of this invention to provide an antenna computing switch which can control the direction of the beam of an array of fixed antennas.

' The invention comprises a plurality of conducting bars connected consecutively to a delayline. arranged in a plane where they are parallel to each other and insulated from each other. A plurality of contacts engage the bars and respectively represent antennas in an array. The contacts have the same relative positions on the bars as do the antennas represented by them with 55 a known proportionality factor. The delay line has one end connected to a receiver or transmitter, as required in a given case.

Further objects, features and advantages of the invention will be apparent to a person skilled in the art 0 upon study of the specification and drawings, in which:

Figure 1 illustrates one form of the invention;

Figure 2 represents an array of omnidirectional antennas and its radiation pattern; and

Figure 3 shows another form of the invention.

Figure 1 represents a computer for determining the radiation pattern for an array of antennas. simplest when omnidirectional component antennas comprise the array, and such antennas are assumed in the example of Figure 1.

A plurality of bars 10 of conducting material aresup- I ported parallel to each other and are insulated from The bars are 50 It operates A 2,866,968 Patented Dec. 30, 1958 ice each other to present a common surface in Figure 1. The edges of the bars are preferably made thin to minimize coupling between them, and a shielding barrier may be provided between them to further reduce coupling, if desired.

A plurality of contacts 11, 12, 13 and 14 mechanically and electrically engage respective bars 10. Each of the contacts represents one antenna, and all of the contacts represent an array, with the contact positions being di- 0 rectly proportional to the positions of antennas in a simulated array.

A signal generator 16 simulates a transmitter and provides energy to the array of contacts. The'output of generator 16 is connected to the respective contacts by transmission lines 21, 22, 23 and 24. Each transmission line has connected serially with it a phase adjuster or line stretcher 26, 27, 28 or 29 to control the phase of energy at its respective contact.

Also, each line includes an attenuator 31, 32, 33 or 34 to control the intensity of the energy at its respective contact.

Each contact is series connected to its transmission line through a resistor 36, that is substantially equal to the characteristic impedance of its transmission line to prevent wave reflection back to generator 16.

Hence, the energies at contacts 11 through 14 are representative of the intensity and phase of energy at the respective antennas in the simulated array. When the attenuators are set to fixed values, the contacts in Figure 1 represent omnidirectional antennas.

A delay line 40 has conducting bars 10 connected consecutively along it at points that present uniform intervals of time delay. Delay line 40 can be either a lumped-constant artificial transmission line or a distributed-constant line.

A detector 41 is connected to one end of delay line 40; and a meter 42, which can be a voltmeter, is connected to the output of detector 41.

To compute the radiation pattern of the simulated array, it is necessary to rotate the given array of contacts relative to the plurality of bars. The contacts may be reset manually at each rotational position; or a jig (not shown in Figure 1) can be provided to maintain a given set of contact positions at each rotational setting.

Readings are taken from meter 42 at different relative rotational positions. Each reading provides the net intensity at one point on a radiation pattern curve that is radially distant from the simulated array. A sufiicient number of meter readings and their respective rotational positions are plotted on polar coordinates, so that a smooth line connecting them represents the radiation pattern of the simulated array. The operation of the invention in Figure 1 may be better understood by first analyzing the radiation pattern of an actual array of antennas shown in Figure 2 that is simulated by the contacts in Figure 1. Thus, contacts 11, 12,13 and 14 are positioned proportionally in regard to the omnidirectional antennas a, b, c and d in Figure 2.

The array in Figure 2 has a radiation pattern 46 that is radially distant from it. Point P is any point on pattern 46. Thus, each point on the pattern is so distant from the array that the respective waves from the component antennas in the array travel in substantially parallel lines to the point.

The energy received at point P comprises the sum of the energies from the component antennas after being differently phase shifted due to the different propagation distances of the antennasfrom point P.

In Figure 2, an arbitrary point 0 is selected within the array, and a line 48 is drawn through points 0 and P.

Thus, waves from the component antennas travel substantially parallel to line OP while propagating to point P. Dashed lines in Figure 2 are drawn perpendicularly from, thecomponent antennasin Figure 2 to line and intersect it at points M,.N, S. and T. Therefore, energy from antenna d substantially travels a distance MP, energy from antenna a substantially travels the.distance NP; radiation from antenna c travels the distance SP; while energy from antenna b travels the distance TP. Therefore, the component energies at point P are delayed differently by amounts proportional to the diiference in distances between points M, N, T andS. Hence, the differences in the delays. caused bythe difierent positions of the antennas are responsible for propagation phase shifts that control. the'net radiation intensity at a point P., Q r

Consequently, at point P in Figure 2 the wave from antenna a travels the distance MN more than the wave from point d :and-is delayed by the time-necessary for it to. propagate distance. MN ata velocity of approximately 3x10 meters per second. Similarly, the waves from antennas b andc travel distances TM and SM, respectively,.more'than thewave from antenna 0.. Accordingly, the distances MN, TM and SM are directly proportional to-specific delay periods and propagation phase shifts.

The component phases at any single distant point P can berepresented mathematically as follows:

Where 4P, 4P, LP and 4P represent the phase angles of the respective waves at point P; L,,, L L and L represent the length of-respective transmission lines connected to the component antennas, A is a Wavelength in each of the transmission lines; D,,, D D and D are the, respective distances of the antennas from an arbitrary point Within the array; a is a wavelength in free spa-ceyande 6 0 and 6;, represent the, angles, of the respective antennas with respect to point O'from a line drawn between points 0 and P.

Then, the net energy intensity (P at point P may be determined as follows:

P AgP 12 1 CAPC DLP where A, B, C and D represent the intensities of the energies at the respectiveantennas in thedirection of point-P.

It is, therefore, noted that the solution required to obtain the intensity of energy at each distant point. on the radiation pattern curve is complex and involves much computation.

The above solution comprehends any number of antennas: A difierent equation of the type given in Expressions 1 through 4 is required for each antenna. solution provided by Expression 5 comprehends the'summation of all the vector intensities at point P. When the. antennas are omnidirectional, intensity values A, B, C and D remain substantially the same for all points-on theradiation pattern. 1

Theinvention shown in Figure 1 instantaneously solves all the above equations to provide'a reading on meter 42 proportional to the net radiation intensity P at; any'point Pfregardlessr ofthe number of antennas in the array or their; relative positions:

The first term on the-right-hand side "of each of Equations: 17 through 4 represents the respective phase shift caused byzthe connected transmission lineand "is -pi'o- The vided in Figure 1 by the adjustment of the respective phaseshifters 26 through 29. The second component on the right side of Equations 1 through 4 represents the space-phase shift at point P due to the positioning of the respective antenna. The bars and delay line provide this solution as explained below.

The component intensities A, B, C and D in Expression 5 are simulated at the contacts, by the'adjustments of respective attenuators 31 through 34.

Accordingly, the adjustment of the attenuators and line phase shifters simulates, the respective phases and intensities of energies at the component antennas represented by the contacts.

The additional phase shift caused at point P by the relative positions of the antennas in the array is provided by the relative positions of the contacts on bars 10 and by delay line 40.

The. energy of any contact is not delayed significantly in traveling from its respective contact to the delay line. Such delay effect is minimized by making delay line 40 with a relatively large amount of delay. The construction of delay lines is Well-known. Thus, delay along the bars is neglected in the operation of the invention. The waves from the contacts are delayed various amounts by the delay line. Thus, the energy from contact 11 is de layed more than the energy from contact 14 by the period MN in the same manner as explained in connection with Figure 2 (except for a small error caused by the incremental variation of' the bars). Contact 12 is delayed by the period TM, and contact 13 is delayed by the period SM. This also corresponds to the solution of the last term on the right in each of the Equations 1 through 4.

Since the energies from the respective contacts are all provided to the delay. line, they are combined vectorially when they have reached output 43 of the delay line. This provides. the summation of Expression 5. Accordingly, meter M'provides a reading proportional to the vectorial sum or net intensity of energy at distant point P.

The bar arrangement only comprehends delay with respect to the array of contacts in a direction that is perpendicular to. the bars. No delay is provide'd'for the distance separations in a direction parallel to the bars. Therefore, pointP' with respect to the array of contacts is on a line perpendicular tothe bars, such as line 48 in Figure 1, and is in' the direction of the receiving end of the delay line. Consequently, as the array of contacts is rotated to different angular positions with respect to the bars, dififerent points on theradiation pattern are obtained. Asmany points can be obtained as desired, and a smooth curve is drawn between them to' provide the radiation pattern of the array.

The, incremental error caused by the finite widthof the bars is decreased by decreasing their width and increasing their number to decrease. the incremental phase shift along the delay line between adjacent bars. When adjacent bars differ in phase by less than ten degrees of wavelengthalong the delay line, the computer yields a very close approximation to the true radiation pattern.

The table of bars has a length D measured between the center-lines of its terminating bars. Length D is pro portionally related to a distance in space with a'proportionality factor K defined as follows:

- space at any given frequency.

There willhe a tota'l time delay t forenergy to. travel albng 3 line between its connection to the term' in 1 7 bars. Then, the total delay time between terminal bars is:

t =(N--l) Vic sec. (7)

in which L and C are the inductance and capacitance of the delay line between any adjacent bar connections, and N is the number of bars.

Thus, the table of bars represents a distance D in free space of:

D =3 X IO t meters (8) Length D should be at least as great as the longest wavelength dimension across a simulated array as viewed on the table of bars.

The frequency f of signal generator 16 is:

D fit m Generally, it should be at least one-half'wavelength R since most simulated arrays have at least this breadth. Generator frequency f also must be a frequency below the cutoff frequency of delay line 40.

In Figure 3, the invention provides a goniometer capable of rotating a radiation pattern 50 of an array 51 of fixed omnidirectional antennas 52 through 59, which are connected through respective amplifiers R by means of respective transmission lines 72 through 79 to bar contacts 62 through 69.

Bars 10 are imbedded in insulating material 60 to provide a smooth surface for a bar table assembly 82 so that the contacts can ride from bar to bar across a bridge of insulating material without mechanical discontinuity. The contacts 72 through 79 are bound together in an insulated manner by mechanical means 81 (shown schematically by dotted lines in Figure 3). The contacts are positioned on the table with wavelengths A equal to the free-space wavelength A, of simulated array 51. Thus, for example, if the antennas in the actual array are arranged in two circles having the radii R and R the contacts on table 10 are positioned with the radii KR and KR;,.

Delay line 40, in Figure 2, which is an artificial line, is connected to bars 10 at points between sections. It is terminated by a resistor 84 that matches the impedance looking into that end of the line, in order to prevent wave reflections from that end. Artificial line 40 is preferably a tapered line, which is a term well-known in the art.

That is, the various sections of the artificial line are made so that the characteristic impedance of the line varies along it from a largest value at the end terminated by resistor 84 to a minimum value at its opposite end, which is connected to a rotating coaxial joint 86. The taper of the characteristic impedance of the line is chosen to provide the optimum impedance match for the multiplecontact connections to the delay line. When the number of contacts is large, a linear taper is satisfactory. Their number varies at any one bar 10 as the table is rotated relative to them. To a degree, the contacts appear in parallel to joint 86.

A single-pole double-throw switch 90 is connected to rotatable joint 86, so that table 82 can be rotated to any position over a range of 360 degrees. Contacts 62 through 69 are non-rotatable in Figure 3. A receiver 91 and a transmitter 92 are connected to opposite contacts of switch 90.

Beam 50 provided by antenna array 51 rotates proportionally with rotation of table 82, and, accordingly, can be positioned to any azimuth angle indicated by calibrating the angular positions of table 82.

Array 51 is initially set up so that its omnidirectional antennas are positioned to provide a required radiation pattern, such as narrow beam 50. The determination of the positions of the component antennas can be conveniently done with a computer of the type illustrated in Figure l.

Once the required pattern is obtained, contacts 62 through 69 are positioned proportionally on table 82.

The computer, comprising the table of bars and the delay line, controls the phasing of energy at the respective antennas, which in the indicated position of Figure 3, provides beam 50 in the direction shown. As table 82 is rotated relative to the array of contacts, it is realized that the phasing provided to the component antennas by the delay line and bars varies accordingly. Beam 50 rotates relatively smoothly and not in increments or jumps, because the incremerital variation due to the bar widths occurs only with a small number of the contacts at any one time during rotation.

By the reciprocity theorem the system shown in Figure 3 may be used for transmitting or receiving, and the rotatable beam from the fixed antenna array can be used with either transmitter 92 or receiver 91 as determined by the position of switch 90. When using the system for transmitting, additional problems occur due to the additional power handled. In such case, the power handled by the delay line and contacts is minimized by having power amplifiers R in the respective transmission lines 72 through 79.

The amplifiers have a further use in the system. When they are located at the antennas, they can present a relatively constant and matching impedance to their respective transmission lines, and can also act as buffers to decouple some of the antenna-coupling variations from the computer.

The antennas simulated by the contacts in the computer need not be omnidirectional antennas. They can have any type of. individual response patterns. However, it is only when the contacts simulate omnidirectional antennas that the attenuators can have a single preadjustment throughout the relative rotation between the contacts and the table.

When the component-simulated antennas have other than omnidirectional patterns, each of their attenuators must be varied to provide an intensity variation in the direction of point P, which in Figure 1 is in the direction of line OP perpendicular to bars 10, to correspond to the intensity variation of the simulated antenna at point P as it is rotated. This can be done by providing for each contact a cam that rotates with table 82. The cam followers are positioned non-rotatably with the contacts. Radial actuation of each cam follower by its cam controls a respective attenuator to provide a contact response that simulates the pattern of its simulated antenna at point P as the table is rotated.

It is, therefore, apparent that'the invention provides a computer which can be utilized in numerous ways, such as for determining the position of component antennas in an array and for rotating the beam of an array of fixed antennas.

Although this invention has been described with respect to particular embodiments thereof, it is not to be so limited as changes and modifications may be made therein which are within the full intended scope of the invention as defined by the appended claims.

What is claimed is:

l. A computing means for an antenna array comprising a plurality of bars of conducting material insulated from each other and arranged with a common surface, a plurality of contacts engaging said bars, with said contacts representing respective antennas in said array, a delay line, with said bars respectively connected to said delay line, means for providing alternating energy to said contacts, and means connected to said delay line for receiving said energy, whereby said delay line provides phase relationship between the energies at the contacts that simulates the space-phase relationship of the antennas in said array.

2. In an antenna computing means for an array of antennas comprising a plurality of bars of conducting material insulated from each other and arranged parallel to each. other, said;bars having their center linesspaced equally, said barshavinga surface: in;.a single plane, a plurality of contactssengaging said: bars, said contactsbeing"positionedwith respect'to cach other with the same spaceproportions as' the antennas in-saidarray; a. delay line; saidbars being connected infsequence' to said-delay line, with said. line providing substantially equal delay between any two adjacent bars connectedzto it.

3. Antenna computingymeansas, definedin: claim 2 comprising mechanical-means for insulatingly fixing to gether said contacts, said mechanical means being rotatable'to rotate said contacts as a group while contacting said bars.

4. Computing means as defined in claim -2 wherein signal-generating means is connected to said contacts, detecting means is connected to one'endn-of saiddelay line, and indicating means is connected to saididetecting means;

5. Computing means as defined in claim 2 comprising a signal generator, a plurality of transmission lines, with each transmission line connected between 'a respective one of said contacts and said signal, generator, a plurality of attenuators, with said attenuators connected respec tively in series with said transmission lines, a plurality of phase-shifting means, with saidiphase-shifting means connected respectively in series with .said transmission lines, means insulatingly supporting said contacts with respect to each other, said plurality of supported contacts being rotatable on said plurality. of -bars,.energy-detecting means being connected to one end of said delay line, and energy-intensity indicating means being connected to the output of said detecting means.

6. Computing means for, an antenna array as defined in claim 5 including means for varying the intensity and phase of energy at the respective contacts with rotation of said contacts to simulate individual directive antenna patterns for the individual antennas represented by said contacts.

7. Antenna computing means as defined in claim 5 comprising a plurality of resistors, with each resistor being connected respectively between one'of said contacts and one of said transmission lines, each resistor having a resistance value substantially equal to the characteristic impedance of one of said transmission lines, and another resistor connected to one end of said delay line to prevent substantial reflection'at that end.

8. Means; for positioni'nggthe. radiation beam of an array of antennas, comprising a plurality of bars of con,- ducting material insulated, from-each other and arranged parallel to each other, said bars having their center lines spaced equally, said bars having a-surface in'asingle plane, apIurality-of contacts engaging said bars on said surface, said contacts being positioned withrespect to each other'with the same proportions asthe antennas in said array, a delay line, said bars being connected in sequence to said delay line, with. said line providing substantially equal delay between anytwo adjacent bars connected to it, said contacts being proportioned according to the delay provided by said d'elay' line,.and a plurality of electrical transmission means connecting the antennas in said array to said contacts respectively.

9. Antenna means as defined in claim 8 in which said radiation beam is rotatable, comprising mechanical means fixing said contacts together in their respective positions andyisolated from each other, said mechanical means being rotatable with respect to saidplurality of bars while maintaining sliding engagement of said contacts' with said bars, whereby the radiation-beam of said array rotates proportionally with relative rotation between said mechanical means and said plurality of bars.

10. An antenna system as defined in claim 9 in which a plurality of buffer amplifiers are respectively included in said plurality of transmission means to isolate impedance variations of said antennas from their respective contacts.

11. An antenna system as defined in claim 10 having a receiver of alternating energy connected to one end of said delay 1ine,;whereby the rotatable directivity of said; antenna, radiation beam controls the intensity of received energy by said receiver.

12. An antenna system as defined in claim 10 in which a transmitter is connected to one end of saiddelay line, whereby the transmitted radiation beam from said antenna array is rotatable proportionally with the relative rotation between said, plurality of bars and said plurality of contacts.

ReferencesCited in the file of thisipatent UNITED STATES PATENTS 2,786,193 Rich Mar. 19, 1957 

